Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
This invention relates -to methods of installing
frames for access pits and manholes, and more particularly
frames for supporting mul~ip:le covers or gratings above
such pits or manholes.
Where an access pi-t or manhole having a clear
opening of relatively large area is -to be provided with a
multiple-cover arrangement capable of withst~n~ing heavy
loads~ i-t is conventional practice to span the opening
by means of one or more I-section s-teel beams (rolled
steel joists) so as to divide the area to be covered into
a nu~ber of smaller areas. Each of these smaller areas
is then covered by a n~ber o~ covers disposed side by
side~ each cover extending between two adjacent beams,
or between a beam and the adjacent wall of the pit, and
being suppor-ted at its ends by parallel frame members, at
least one of which is supported on the upper surface o~
a beam. Where two covers are posi-tioned symme-trically
on ei-ther side of the centre line of a supporting beam,
the beam carries a separate frame member for each cover,
the two frame members being supported by the two upper
flanges re~;pecti~ely o~ the beam~ There is normally
a gap between the two adjacent frame members which is
filled with concrete in order -to increase the rigidity
o~ the s-tructure.
~.
However, where such covers are to be subjec-ted
to high loads, for example in docks~ airports and general
heavy traffic areas, the upper flanges on the beam may
become de~ormed by excessive :Loading o~ the ~rames.
This may result in the beams becoming eccentrically
loaded leading possibly to fa:ilure o~ the beams.
It is an object of -the invention to obviate
these disad~antages by using an entirely novel installa-tion
method which ensures that eccentric loading of the beams
does not occur under heavy load.ing condi-tions.
SUMMARY OF THE IN~ENTION
According to the invention there is provided
a method of inst~11 ing frames for supporting multiple
covers or gratings above an access pit or manhole,
comprising sp~nn; ng the clear opening o~ the pit or
manhole by m0ans o~ at least one support beam so as to
divide the total clear area into smaller areas each of
which is to be covered by a number o~ separate covers or
gratings, and laying on the or each support beam one or
more frame members each of which is shaped 50 as to
support parts of two covers or grating which are adjacent
and on opposite sides of the beam.
Where the support beam is of` I-section, the
longi-tudinal axis of the frame member should be posi-tioned
directly above the centre line o~ the beam, so that
~orces acting on the ~rame member are -transmi-tted
vertically cLownwards through the centre line so that
the support beam is symmetrically loaded at all -times,
even under heavy loading conditions.
- 3
Advantageously a frame member is used having
-two inclined seating faces vn opposite sides of the
member each of which i5 intended -to engage a correspondingly
inclined face on a respective one of the adjacent covers
or gratings -to support said cover or grating. These
inclined seating faces serve to distribute the load
along the ~rame member.
Furthermore -the frame member preferably includes
two ~eating blocks at opposite ends of the member each of`
which has an angled seating face facing in the general
direction of the opposite end of the member and intended
to engage correspon~ingly angled faces on the adjacent
covers or gra-tings.
The invention also provides a multiple cover
or grating installation above an access pi-t or manhole, in
which at least one support beam spans the clear opening
of the pit or manhole so as to divide the total clear area
into smaller areas each of which is covered by a number of
separate covers or gratings, and one or more frame members
rest on the or each support beam, and are each shaped so
as to support parts of -two covers or gratings which
are adjacent and on opposite sides of the beam.
The invention includes within its scope a ~rame
member for use in methods or installations according to
the invention~ as hereinbefore described.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the inver~ion may be more fully
understood, two installations in accordance with the
invention will now be described~ by way of example, with
reference to the accompanying drawings, in which:
Figure 1 is a perspective view of a frame member
and cover on a support beam in a ~irst installa-tion;
Figure 2 is a vîew of the ~rame member and cover
o~ Figure 1 from one side, prior to ~itting of the cover;
and
Figure 3 is a perspective view of a frame member
on a support beam in a seconcL installation.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring to Figure 1 the support beam 2 is a
rolled steel joist (RSJ~ of I-section and includes a
central support web 4, upper .flanges 5 and 6 and lower
flanges (not shown). Referring also to Figure 2, the
frame member 10 has two inclined seating faces 11 and 1~
each of which is provided for supporting a respective one
of two adjacent covers such as 140 The frame member 10
also includes at its ends two seating blocks 15 and 16
each of which is provided with two fl~nges 17 and 18 which
are attached to the support beam 2 by bolts (not shown).
The seating blocks 15 and 16 have angled seating faces
19 and 20 each of which provides suppor-t for both of the
adjacent covers such as 14.
The covers are shaped so that, when they are
engaged with the frame member 10, the edges of the covers
~Lg~
are substantially contiguous. Each cover is provided with
inclined faces 21 and 22 for engaging with one of the
inclined seating faces 11 or 12 on the frame member 10.
The cover 14 is shown sligh-tly raised in Figure 1 so that
these faces 21 and 22 are visible. In addition each
cover is provided with angled faces 23 and 24 for engaging
wlth the angled seating faces 19 and 20 on -the seating
blocks 15 and 16 of the frame member 10. Both covers
also incorporate re-entrant corners ~5 and 26 ~or
accommodating the seating blocks 15 and 16 9 numerous
strengthening ribs such as 28 and 29, and a recess 30 for
enabling the cover to be lifted.
Where a pit or manhole having a clear opening
of relatively large area is to be covered by such an
arrangement, the opening is spanned by a number of
support beams arranged parallel to one another and spaced apart
by a distance corresponding to the leng-ths of the covers.
Frame members such a~ 10 for supporting the covers are
then laid end to end along the beams and bolted to the
beams. Finally the covers are disposed side by side in
rows between the beams so that each cover is suppor-ted by
a respective frame member at each of its ends and
adjacen-t covers in the same row abut each other along
their sides. Adjacen-t covers in adjacent rows are both
supported by the same double-sided frame member.
In the installation shown in Figure 3 the frame
member 10 is slightly di~ferent in construction to the
frame member o~ Figure.s 1 and 2. In particular each
~ 6 --
seating block 15 or 16 is provided with only a single
flange 31 or 32, and the ~lange 31 on -the seating
block 15 e~tends from one side of -the frame member 10
whilst the flange 32 on the seating block 16 extends
from the other side o~ the frame member 10. The frame
member 10 is fi~ed to the suppor-t beam 2 by means of
bolts (not shown) passing through the flanges 31 and 32
so that its longitudinal axis lies directly above the
centre line of the beam 2 and in particular so that the
longitudinal axis of the ~rame member 10 lies in a
vertical plane 34 within which the support web 4 of the
beam 2 extends.
The support beam 2 spans the clear opening of
a pi-t 36 and is welded at each end to a thick stiffening
~5 plate 38 and a wall box 40 fixed to the side of the
pit 36. In addition angle side frame members 42 are
attached to the edges of the pit 36 for supporting the
sides of the covers closest to the sides o~ the pi-t.
In both embodiments described above with
reference to the drawings the frame member is cast by the
mono block process from spheroidal graphite iron. This
enables the frame member to be cast -to very high
tolerances so that an accurate fit with the matching
cover or grating (also made from spheroidal graphite
iron) is ensured.
